Computed tomography (CT) is an X-ray examination method whereby sectional images, so-called slices, are taken of the body of a patient by letting an X-ray tube device rotate 360 degrees about the patient. The patient is located on a moveable table which moves in incremental steps slowly through an opening or tunnel where the X-ray tube device rotates about the tunnel. The body of the patient is thereby sectioned by a CT computer approximately like cutting a bread in slices. Each of these slices are then viewed by an operator on a display. The slice images are taken at right angles to the longitudinal axis of the patient body, and each image has a number corresponding to an address along the longitudinal axis (z-axis). It is possible to select both the thickness of the slices and the interdistance between the slices. The normal slice thickness is 7 or 10 millimetres thickness edge-to-edge.
It is sometimes necessary to introduce a thin instrument needle into a patient and towards a region to be investigated, and e.g. remove some tissue cells in order to establish whether e.g. a malignant tumour is present. If such tumour is large and close to the skin surface, such biopsy procedure is normally not complicated. However, if the tumour is small and/or lies deeply inside the body, it will be appreciated that it can be very difficult to hit the target tumour exactly with the needle.
Present day practice is that first, a series of computed tomography slice images are made of the patient. Thereafter, the various images to be shown on the display are searched until an image is found where the tumour is clearly shown.
Thereafter, an electronic marking is made on the display corresponding to the spot on the skin where it is desired to have the point of insertion, e.g. 5 centimetres to the right of a centreline. Thereafter, the patient table is moved to the address or table position on the image in question, and by means of a guide light, a line is drawn transversely of the body of the patient, corresponding to the longitudinal axis address of the image in question. It is then measured by means of a ruler 5 centimetres to right from the centreline, and a marking is made thereat on the body. At that marking there is placed a small metal indicator, e.g. the point of a syringe which is attached to the skin by means of adhesive tape and parallel to the longitudinal axis of the patient body. Again, the image in question is taken, and at this occasion the metal indicator will appear on the image at the intended point of insertion, and it is thereby possible to check that the point of insertion corresponds to that which was intended.
The next step is to place two electronic crosses on the display, one at the point of insertion and one at the tumour. The CT computer will then calculate the distance between the two points and the angle therebetween. The distance may e.g. be 7.5 cm, and the angle e.g. 21.5 degrees to the right relative to the vertical. Local anaesthetics is applied to the region of the point of insertion, and an instrument needle is thereafter moved 7.5 cm into the patient body.
One substantial drawback of such procedure is that the proper angle when inserting the needle has to be determined by the radiologist more or less by eye measure. Using devices which can be placed on the human body and in physical contact with the instrument and its needle are cumbersome in use, inaccurate and must be thoroughly desinfected after used or be of a single use type. Such devices are therefore expensive in use, and the risk of infection is present, unless absolute sterile conditions are present during the repeated attempts to hit the target, e.g. a tumour.
Therefore, in practice, the radiologist more than often simply determines the angle of the insertion of the needle based on eye measure judgement only. As will be appreciated, it is not at all easy to introduce a needle at an exact angle of 21.5 degrees based on eye measure only. In addition, the insertion is to be made in a plane exactly 90 degrees to the longitudinal axis of the patient body. Thus, using the present day method of so-called free-hand puncture it is frequently required to make several puncture attempts before the target is hit. After each puncture attempt, new slice images must be taken to check whether the needle point of the instrument has hit the target or not. Sometimes, it is experienced that the instrument needle has not been introduced into the body in plane 90 degrees to the longitudinal axis of the patient body, and the needle can thereby have moved out of the slice plane. It will be recognised by any surgeon that difficult puncture operations are extremely time-consuming, and in the worst case may take more than an hour. This yields an increased risk of complications, such as internal bleedings, in addition to the obvious discomfort of the patient. Further, a computed tomography machine is a very expensive device which costs approximately one million US dollars or more. Thus, the cost of using a machine per time unit is important. Therefore, this is more than often a problem in the medical examination process within a hospital, and time consuming attempts to hit the target within the patient body may occupy the CT-machine for an unacceptable long period of time.
In order to solve the problem of introducing the instrument needle into the patient body at a correct angle, some hospitals use different types of puncture accessories, both mechanical and optical. In practice, they are not widely used, simply because their operation is somewhat cumbersome.
From the prior art there are known many methods and apparatus for assisting percutaneous computed tomography-guided surgical activity inside a human or animal body. Many apparatus and methods, however, strongly rely on the apparatus being clamped onto the human body, e.g. the head of a human, such as described e.g. in U.S. Pat. No. 5,116,344. Other devices such as that described in Austrian patent 387903 rely on the apparatus being attached to the human body at the insertion point and with the needle type surgical instrument extending through a guide tube of the apparatus. Such an apparatus requires either thorough cleaning after use or that the apparatus is simply a single-use apparatus, which makes it rather expensive.
U.S. Pat. No. 4,733,661 relates to a hand-held apparatus for insertion of the surgical instrument, but is difficult to use, because the surgeon must use one hand on the apparatus and one hand on the surgical instrument to be inserted, which may prove difficult in practice.
Also, the surgical instrument is in contact with the device and thorough cleaning of the device after use is absolutely required.
U.S. Pat. No. 5,308,352 relates to a stereotactic device supported by a frame structure over the platform on which the human or animal body is placed. The device is put into a physical contact with the body and in that position clamped to the supporting frame. Thereafter, the surgical instrument is inserted into the body through a pair of guide holes. Thus, the stereotactic device according to U.S. Pat. No. 5,308,352 also requires thorough cleaning after use, which makes it complicated and expensive for practical purposes.
A stereotactic instrument similar to that of U.S. Pat. No. 4,733,661 is also known from European patent publication 0414130. However, the same deficiencies as with other prior art devices of the same type also apply to that of European patent application 041430.
The present invention, however, is intended to provide a method and an apparatus in which the assistance in the surgical activity is based on a non-physical contact between the apparatus and the human or animal body or between the apparatus and the needle-type surgical instrument to be inserted into said body.